“Skin-like” tactile sensors are known for applications in the field of humanoid robotics, where they are applied on the rigid outer part of a robot body (shell) to provide information about the contact between robot and environment. Particularly, such sensors allow detecting the pressure exerted by an object, the environment, or a human being, on the coated areas of the robot, and allow defining the shape of an object contacting the same robot.
Sensor arrangements having suitable geometrical structures can be also applied on curved surfaces of a robot shell, thus fitting thereto, leaving not covered only a minimum part of the robot, essentially the articulation joints.
It is of course desirable to have a large high-resolution “sensitive” surface, which can be obtained by providing a sensor arrangement as much drawn closer as possible, without unduly increasing the relative electronic control complexity.
JP 2006-287520 discloses a communication network for artificial skin, based on the connection of modular patches, each comprising at least one tactile sensor, and a microcontroller unit, so as to obtain a logic network of sensors capable of sending the tactile information acquired from any node to a central processor controlling the robot. Each node is physically connected to at least another node and at most four nodes. At a physical level, the network is completely connected. At a logic level, the techniques employed in the field of processor networks (Dynamic Source Routing Protocol) are used in order to reconstruct network topology.
Advantageously, innumerable patches can be connected one another without paying attention to the network topology, which will be recreated subsequently.
However, this solution has the drawback that each patch is very complex from the point of view of the required electronic components, therefore the relative cost is high, and the energy consumption is not negligible. Furthermore, many connections between the various nodes have to be physically implemented, and this makes data routing particularly complex.
JP 2002-352370 discloses the implementation of a “strip” of tactile sensors arranged on a film, adapted to the wireless transmission of the pressure data detected. In this case, there are not patch structures comprising more sensors, but all the sensors are mutually connected so as to be able to be supplied, via the supply tracks existing on the film. Instead, communication takes place via radio.
Disadvantageously, the environment surrounding the robot is typically very noisy, due to the electromagnetic interferences originating from the robot motors, and this makes radio communication of information difficult, where the number of the pieces of information is high, while the available radio band is reduced.
The article by T. Hoshi and H. Shinoda, “Robot Skin Base on Touch-Area-Sensitive Tac-tile Element,” published in “Proceedings of the 2006 IEEE International Conference on Robotics and Automation”, Orlando, Fla., May 2006, discloses a tactile sensor system in which the sensitive element is used as a transducer and communication means. Each sensor element is connected to the other sensor elements through a communication micro-circuit, the role of which is to condition the measurement signal coming from the tactile element and send it to an external processor. Each tactile element is used both as a transducer and as an electrical connection between the various communication microcircuits, which promotes the signal routing. Disadvantageously, the implementation of this structure is particularly complex (in fact, it is necessary to manage the commutation between detecting condition and data transmission condition) and the spatial resolution is quite reduced.
The article by Y. Ohmura, Y. Kuniyoshi, and A. Nagakubo “Comformable and Scalable Tactile Sensor Skin for Curved Surfaces,” published in “Proceedings of the 2006 IEEE International Conference on Robotics and Automation”, Orlando, Fla., May 2006, discloses an optical tactile sensor formed by LED-photodetector pairs implemented on a flexible substrate, which are adapted to detect the variation in refraction of light emitted by the LED as a function of the mechanical deformation experienced by the sensor contact layer.
More sensor elements are obtained on flexible printed circuit sheets, and the arrangement thereof has a particular geometry capable of coating three-dimensional, thus curved, surfaces. On the whole, each sheet is of a rectangular shape, and having a dimension of 120×200 mm, on which 32 sensor elements are arranged. The sheets can be freely folded and cut, and connected one to the other. Each sheet is provided with a microcontroller which is adapted to manage the measurement data acquisition from the sensor elements, and respective contact terminals for the connection between contiguous sheets are present at the end edges.
From the point of view of the circuit architecture, each sheet is adapted to collect 32 8-bit pressure data. The various sheets are mutually connected via a serial communication bus which is controlled by a master microcontroller arranged on an electronic board managing the assignation to the various sheets in order to sequentially collect all the detected data. In turn, the master microcontrollers are connected one to the other, and to a central processor which controls the robot via a LIN network.
Each contact terminal of the individual sheets can be considered as a data input or output port, with the drawback of being able to constitute, with the serial communication bus, transmission loops which cause electrical reflections on the bus, which are aggravated by the fact that the bus does not have a termination, leading to the bus performance degradation.
Although the use of a flexible printed circuit as a substrate reduces the problem of the data routing, thanks to the fact that the connections are implemented via the same substrate, the spatial resolution which can be achieved is quite low, it being impossible to increase the achieved density of 32 sensors in an area of 120×200 mm according to the proposed architecture, due to the large dimensions of the constituent components of the sensor, the increase of electrical connections which would be required therebetween and, not last, the high need for power supply.
Furthermore, the particular technological implementation of the sensor elements does not allow a simultaneous reading of the measurement data of the same, since the microcontroller sequentially performs the data collection from the various sheets, in order to limit the energy consumption for the device. This makes so that it is impossible to get an average measurement of the data coming from the sensors, but with a post-processing of the same data.
Therefore, the aim of the present invention is to provide a satisfactory solution to the problems set forth above, thus avoiding the drawbacks of the prior art.
Particularly, the aim of the present invention is to provide an arrangement of tactile sensors which is applicable to arbitrarily curved extended surfaces, with sensing devices (transducers) having reduced dimensions, in order to achieve a high resolution, which minimizes at the most the electronic control architecture overall dimensions in the installation on robots and the energy consumption.
A further object is to provide an arrangement of tactile sensors which has a wide range of sensitivity for the detection of both light and heavy contacts, that is, equal to the total body weight of the robot, as well as which is resistant against impacts and shear forces which the robot body can experience.
According to the present invention, such object is achieved thanks to an arrangement of tactile sensors having the characteristics set forth in claim 1.
Particular embodiments are the subject of the dependant claims.